The present invention relates to an improved alkylation process. In particular, this invention relates to a strong acid catalyzed reaction wherein an alkylatable hydrocarbon is alkylated with an olefin to form alkylate hydrocarbons. More particularly, the present invention relates to strong acid catalyzed alkylation of isoparaffin hydrocarbons with olefin hydrocarbons to form highly branched alkylate hydrocarbons suitable for use in the blending of gasoline.
Alkylation processes for reaction of alkylatable hydrocarbons with olefin hydrocarbons are well known and practiced widely upon a commercial basis. Commonly, an alkylatable hydrocarbon such as an isoparaffin or aromatic is reacted in the liquid phase with an olefin hydrocarbon in the presence of a heterogeneous, liquid-phase strong acid catalyst. Of particular commercial importance is the alkylation of low boiling isoparaffin hydrocarbons such as isobutane, isopentane, isohexane, etc. with low boiling olefin hydrocarbons such as propylene, butylenes, isobutylenes, etc., to form high octane alkylate hydrocarbons suitable for use as gasoline blend stocks. The reactants may not be normally liquid, consequently, superatmospheric pressures are commonly employed to maintain reactants in the liquid phase. Reaction temperatures are preferably in the range of below 0.degree. to 150.degree.F. Strong acid catalysts, such as sulfuric acid, fluorosulfonic acid, mixtures thereof, and hydrogen fluoride, are commonly employed in commercial processes. The catalyst used is brought into intimate contact with reactants by agitation or other mixing means. Under such reaction conditions, olefin hydrocarbons tend to react together forming polymer compounds as well as reacting with isoparaffin hydrocarbons to form the desired isoparaffin-olefin alkylation product. Such olefin polymer by-products also tend to crack in the presence of the strong acid catalyst thus forming undesirable low octane light alkylate as well as equally undesirable high molecular weight heavy alkylate compounds. Additionally, olefin polymers are difficult to separate from the strong acid catalyst and form acid-oil sludges therein. The presence of such acid-oil sludges as well as water in the strong acid catalyst decreases the strength of the strong acid catalyst. Such decrease in acid catalyst strength contributes to an increase in undesirable side reactions, such as olefin polymerization as well as decreasing the effectiveness of the acid catalyst for alkylation of isoparaffin with olefins.
Desirably, the alkylate product comprises a major portion of the highly branched isomers of the isoparaffin-olefin alkylation reaction product. For example, in the alkylation of isobutane with butene, trimethylpentanes are the desired product, and in the alkylation of isobutane with propylene, dimethylpentanes are the desired product. Low catalyst acidity due to the presence of acid-oil sludges and water contributes to production of less highly branched alkylate isomers which have lower octane values than more highly branched isomers, and consequently are of less value in gasoline blending. Additionally, cracked olefin polymers contribute substantial amounts of undesirable light and heavy alkylate compounds which have substantially lower octane values than the highly branched isoparaffin-olefin alkylation products.
It is known that surface active compounds may be employed in admixture with strong acid catalysts in an alkylation process to improve the production of highly branched isoparaffin-olefin alkylation products at the expense of olefin polymers and the resulting light and heavy alkylate compounds. Also, the use of surface active agents decreases the consumption of acid catalyst in an alkylation process. For example reference may be made to the following U.S. Patents which describe a variety of surface active compounds which may be used in alkylation processes described herein: U.S. Pat. Nos. 2,880,255; 3,551,514; 2,981,772; 3,231,633; 3,364,280; and 3,324,196. Such surface active agents, disclosed in the preceding patents, are effective for reducing the surface tension of the strong acid catalyst thereby improving contact of the catalyst with reactant hydrocarbons. It is also postulated that perhaps these surface active agents may serve to increase solubility of reactant hydrocarbons within the liquid catalyst phase. As a consequence, such surface active agents must be used with care since relatively small amounts tend to create stable emulsions of reactant hydrocarbon and acid catalyst under the conditions of agitation and mixing commonly employed in commercial alkylation reactions. Such reactant acid emulsions are difficult to break thus complicating separation of acid catalyst from hydrocarbon effluent of an alkylation process.